Pseudomonas

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Pseudomonas

In this article

Pseudomonas spp. are Gram-negative rod bacteria commonly found in soil, ground water, plants and animals. Pseudomonal infection causes a necrotising inflammation. Between 2008 to 2012, there was a 6% decrease in the number of Pseudomonas spp. bacteraemias reported to Public Health England (PHE) compared with a 1% decrease for all bacteraemias. The overall incidence in 2012 for Pseudomonas spp. bacteraemias was 6.4 cases/100,000 population in England, Wales and Northern Ireland. Pseudomonas aeruginosa is the most common cause of pseudomonal infection.[1]

Pseudomonads include a number of true Pseudomonas species as well as many species formerly classified in the genus.

Pseudomonads are natural residents of soil and water and may cause primary skin infections in healthy individuals, usually a self-limiting skin rash or folliculitis.

In immunocompromised patients, systemic infections can occur which may be severe and associated with a high mortality.

The genus Pseudomonas once comprised over 100 species but over the period of a decade many of these have been reclassified into different genera. The main groups of pseudomonads of medical interest are:

Within this genus, there are at least 30 species in the genus but the medically important species are B. cepacia, B. pseudomallei and B. mallei, which are are associated with human and animal infection.

B. cepacia is an important pathogen of pulmonary infections in people with cystic fibrosis.

B. pseudomallei is the causal agent of melioidosis, a life-threatening septic infection prevalent in Southeast Asia and Northern Australia.

B. mallei causes glanders, a rare disease in horses and other species.

Both B. pseudomallei and B. mallei must be handled in category 3 containment facilities and their exchange between laboratories is restricted.

Delftia acidovorans:

Occasionally found in clinical specimens and the hospital environment.

Brevundimonas spp.:

B. diminuta and B. vesicularis are rare in clinical specimens and of doubtful clinical significance.

Stenotrophomonas maltophilia:

May be clinically significant in severely immunocompromised patients and is increasingly isolated from sputum of patients with cystic fibrosis.

The overall incidence in 2011 for S. maltophilia bacteraemia was 0.8 cases/100,000 population in England, Wales and Northern Ireland.

Sphingomonas paucimobilis:

S. paucimobilis has been found in clinical material and recovered from hospital equipment.

The rest of this article is specific for infections caused by P. aeruginosa.

Pseudomonas aeruginosa

P. aeruginosa is an opportunistic pathogen that can cause a wide range of infections, especially in immunocompromised people and people with severe burns, diabetes mellitus or cystic fibrosis. P. aeruginosa is relatively resistant to many antibiotics but effective antibiotics include imipenem , meropenem, ceftazidime, ciprofloxacin and gentamicin. Resistance to piperacillin/tazobactam increased by 3% (from 6% to 9%) between 2008 and 2012.[1]

P. aeruginosa is also a frequent cause of chronic respiratory infection in patients with cystic fibrosis. As many as 80% of cystic fibrosis patients may be colonised in the lung with P. aeruginosa and, once established, it is very resistant to antibiotic treatment.

Gastrointestinal

Pseudomonas spp. typhlitis most often occurs in patients with neutropenia and presents with a sudden onset of fever, abdominal distension and increasing abdominal pain.

Urinary tract infections

Urinary tract infections are usually hospital-acquired and related to catheterisation or surgery.

Severe infections may lead to renal abscess and bacteraemia.

Skin

Green nail syndrome: may develop in people whose hands are frequently immersed in water.

Secondary infections can occur in patients with eczema and tinea pedis; presents with a blue-green exudate with a fruity odour. Is also an important cause of secondary infection of burns.

Common cause of whirlpool or swimming pool folliculitis: pruritic follicular, maculopapular, vesicular or pustular lesions occur where the body has been immersed in water. May lead to subcutaneous nodules, deep abscesses, cellulitis and fasciitis.

Suppurative thrombophlebitis may originate from an intravenous cannula in situ.

Investigations

Blood cultures.

Local investigations, dependent on the site of infection - eg, CXR, sputum, stool, urine cultures.

Management

Most infections are susceptible to third-generation cephalosporins (ceftazidime), carbapenems (imipenem and meropenem), aminoglycosides (gentamicin and tobramycin) and colistin.[1]

Serious infections are usually treated with ticarcillin or piperacillin, often in combination with an aminoglycoside.[1]

Nebulised antipseudomonal antibiotic treatment (tobramycin or colomycin) has been shown to be effective and improve lung function in patients with cystic fibrosis. However, the overall benefits and long-term adverse effects are still uncertain.[3]There is some evidence that oral antibiotics may work just as well.[4]

Ceftazidime is very effective for pseudomonal meningitis because of its high penetration into the subarachnoid space.[5]

Malignant otitis externa requires aggressive treatment with systemic combinations of antibiotics and surgery. Duration of treatment is 4-8 weeks, depending on the extent of involvement.[6]

Eye infections: in cases of small superficial ulcers, topical therapy, consisting of an ophthalmic aminoglycoside or quinolone antibiotic is an alternative. Endophthalmitis requires aggressive antibiotic therapy (parenteral, topical and intraocular).

Urinary tract infections: piperacillin/tazobactam combination or an aminoglycoside are the antibiotics of choice for severe infection. These drugs have a synergistic effect and can be given together.[7]Ciprofloxacin continues to be a preferred oral agent.

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